Using simple phenomenological models for the properties of 1G+1G , 1G+2G , and 2G+2G  binaries, we perform hierarchical inference to determine the properties and rates of these different subpopulations.
These phenomenological models are a natural extension of previous studies of the mass and spin distributions of binary black holes [1]}, [2]}, [3]}, [4]} and are explained in Sec. .
The hierarchical inference methodology using these models is explained in Sec. .
We apply our methodology to the set of binary black holes presented in GWTC-1 [5]} in Sec. , and discuss the inferred population hyperparameters in Appendix .
In Appendix , we consider how results change upon adding GW190412 [6]} to the GWTC-1 population.
In future work, we will extend this analysis to events found by external searches [7]}, [8]}, [9]}, [10]}, [11]}.
We find that observations are consistent with all binaries being 1G+1G  [12]}, [13]}, [14]};
however, if we include the possibility that some 1G  black holes are born with near-zero spins [15]}, [16]}, [17]}, we find a small probability of GW170729 containing a 2G  black hole using our models for globular clusters.
Our conclusions are summarized in Sec. .
